Assessment (as of 30 May 2019):
- In the past month or so, sea surface temperatures of the central and eastern equatorial Pacific remained above normal. Based on the latest oceanic observations as well as forecasts by a number of climate models around the world, the El Niño is expected to persist through this summer. According to statistical analysis, the summer temperature of Hong Kong is more or less the same during El Niño and the ENSO-neutral state. However, the summer rainfall is generally slightly lower in the former case than the latter, though the difference is not significant. Climate models around the world generally forecast that the atmospheric circulation over the northern part of the South China Sea this summer is not totally consistent with the general situation during El Niño. Based on these considerations, it appears that El Niño is not a critical factor in affecting the weather over Hong Kong in this summer.
- Under the influence of global warming and local urbanization, summer temperatures in Hong Kong exhibit a significant long-term rising trend. Climate models around the world also forecast normal to above-normal temperatures over southern China this summer.
- Climate models around the world generally forecast that there will be enhanced moisture transport to the south China coast this summer and hence more rainfall over the region. The forecasts by climate models are consistent with the forecasts given by other objective statistical methods. Hence, a slightly higher chance for normal to above-normal rainfall in Hong Kong is expected.
- Climate prediction centres around the world generate seasonal forecasts, employing a variety of methods including
dynamical models, statistical methods, expert judgment and combinations of them. Predictions from different centres do
not always agree and large discrepancies can occur at times. The Observatory adopts an ensemble approach to formulate
its seasonal forecast for Hong Kong, taking into consideration available products from major climate prediction centres
and the Global-Regional Climate Model (G-RCM) operated in house. Thus,
the resulting forecast issued by the Observatory may be different from the forecast given by G-RCM.
- The Observatory gratefully acknowledges the Tokyo Climate Center of the Japan Meteorological Agency and the National
Centers for Environmental Prediction of National Oceanic and Atmospheric Administration, USA for providing dynamical
prediction model forecast and hindcast data to support the formulation of seasonal forecast for Hong Kong.
- Forecast for autumn 2019 (September to November 2019) will be available around 1st September 2019.
Seasonal forecast charts provided by G-RCM and major climate centres: